In the semiconductor manufacturing, progress is measured in terms of the industry's continued ability to adhere to Moore's Law, which states that the number of transistors on a chip doubles about every two years. The International Technology Roadmap for Semiconductors (ITRS) dictates expected performance specifications for chip manufacturing technology to ensure continued adherence to this law. Accomplishing these specifications in turn requires the development and perfection of new technologies at a pace that is unmatched by any other industry. Among the technical challenges facing the semiconductor industry, lithography presents some of the most formidable problems, particularly the search for a next generation lithography solution that can provide for high-volume manufacturing of computer chips at the 32 nm node and beyond.
Extreme Ultra-Violet Lithography (EUVL) is the leading candidate to succeed optical lithography at the currently used wavelength of 193 nm. EUVL uses a 13.5 nm radiation for forming the circuit pattern image with much higher resolution. This EUV radiation will be absorbed by all materials and hence conventional refractive optics cannot be employed for this lithography technique. Hence these EUVL systems have to use projection or reflective optics. These projection optics require a substrate, on which reflecting layers are applied to reflect the EUV radiation. The most critical requirement for these substrates is near zero (less than 10 parts per billion) thermal expansion properties at the operating temperature of the EUVL systems.
The EUVL scanners, which produce the integrated chips, are being produced in small scale to demonstrate this new technology and the optics systems are an important part of these scanners. Initially, glass ceramic materials were considered and tried for the optics system parts. Currently silica-titania glass, which exhibits a combination of good thermal expansion and an ability to be polished to low high spatial frequency roughness is being used for making the substrates for these optics and optical systems. The advantages of silica titania glass are polishability to the required finish, CTE (Coefficient of Thermal Expansion) control, dimensional stability and radiation stability. The specifications in the EUVL area are becoming more stringent for the newer optics systems, especially the tolerance for Tzc (zero crossover temperature), the expansivity slope (slope of the CTE vs. temperature curve) or temperature width in which the CTE is zero and Tzc spatial homogeneity. This application discloses a silica-titania glass having an additional dopant to further control the expansivity or the temperature width in which the CTE is zero and to a method of making such glass.